I have CommunigatePro v5.1.14 server on a multihomed Windows 2003 server
that serves several domains. Let's say the primary domain is 'main.net'.

I have a subdomain on this server, 'subdomain.net', which sends email using
an address separate from main.net. So, for example:

main.net sends and receives on 1.2.3.4

subdomain.net sends and receives on 1.2.3.7

Reverse DNS for each domain points at the appropriate IP.

When main.net sends email on 1.2.3.4, all is well. However, when
subdomain.net sends email on 1.2.3.7, this appears in the received headers:

Received: from main.net ([1.2.3.7] RDNS failed) by receiver.net with

Microsoft SMTPSVC(6.0.3790.1830); Sat, 15 Mar 2008 00:15:41 -0500

A message actually sent from main.net instead of subdomain.net is ok:

Received: from main.net ([1.2.3.4]) by receiver.net with

Microsoft SMTPSVC(6.0.3790.1830); Sat, 15 Mar 2008 00:17:43 -0500

In a brief exchange with support, I was told that the server always
identifies itself using the primary licensed domain, so I gather that the
receiving server did an reverse DNS check on 'main.net', rather than
'subdomain.net' and discovered the IP didn't match, hence the warning.

Support also told me that there is no way to change how the server
identifies itself, as it's a licensing issue.

So, how do you folks who serve multiple domains handle this situation? I do
have correct SPF records for each domain. I do want to send from separate
domains because the 'main.net' domain is listed in the senderbase reputation
service and I don't want to risk having a subdomain that's not completely
under my control damaging this sender's reputation.